Hammer drills are power tools that have an electric motor that drives a hollow piston. A ram is disposed in the hollow piston and is caused to reciprocate under an air spring effect such that the ram strikes a beat piece in order to cause a hammer action.
The vibration caused by the bit of the hammer drill impacting on a surface can be transmitted to the user, which can be detrimental to the health of the user. Consequently, several solutions to this problem have been proposed.
U.S. Pat. No. 5,947,211 describes a vibration-damped hammer which has a machine housing that holds a drive motor and hammer mechanism to cause a hammering action. A carrier device comprising a frame structure forms a handle for a user, and is mounted by four leaf springs to the machine housing. The leaf springs act to absorb vibrations caused by the hammer bit, and reduce the amount of vibration transmitted to the arms of the user. Two shoulders are formed on the carrier device and are adapted to abut respective stop members formed on the machine housing to limit the amount of travel between the machine housing and the carrier device.
The vibration-damped tool of U.S. Pat. No. 5,947,211 suffers from the drawback that it is difficult for the user to accurately direct the bit of the tool as the shoulders and stop members do not guide the carrier device relative to the machine housing during operation.
U.S. Pat. No. 6,776,245 describes a handheld electrical power tool having percussion mechanism which is displaceable relative to the outer housing. The percussion assembly is mounted on springs so that the percussion assembly can oscillate relative to the outer housing to reduce the transmission of vibrations to the outer housing.
The power tool of U.S. Pat. No. 6,776,245 suffers from the drawback that when the tool is in operation and the percussion mechanism is vibrating relative to the outer housing, it is difficult for the user to accurately direct the bit of the tool.
United States patent application publication no. 2004/0154813 describes a handheld percussion power tool having a percussion unit that is moveable relative to the tool housing. The percussion unit is supported by a coil spring and two flexible articulated arms that enable the percussion unit to move relative to the tool housing to reduce the amount of vibration transmitted to the user.
The handheld percussion power tool of US2004/0154813 suffers from the drawback that when the tool is in use and the percussion unit is moving relative to the housing, it is difficult for the user to accurately direct the bit of the tool due to the free-floating nature of the percussion unit.
Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.